Modern aircraft include various different systems of pipes, conduits, instruments, and accessories in which various liquid products are transported. These liquid-containing components are subject to freezing temperatures during the operation of the aircraft. Therefore, it has become generally known to apply interconnected heater bands, cables, tapes, or strips (generally called heater bands herein) onto these liquid-containing components to provide frost protection. The interconnected heater bands form a heating conductor interconnection system, which is provided with electrical energy from the on-board electrical power network of the aircraft.
The known techniques for interconnecting the several heater bands involve carrying out various prescribed steps to prepare and connect the connection ends of the individual heater bands to further heater bands or to the on-board power supply network. These steps typically involve exposing the electrical conductors of the heater band by at least partially stripping the outer and inner sheaths thereof, whereby the heater element itself is made correspondingly shorter. Generally, the conductors have a length sufficient to serve as extension cables for interconnecting several heating conductors as desired. Next, an adhesive potting or sealing compound is applied over the insulation of the conductors, and then a shrinkable tubing is pushed over the insulation of the conductors and the adhesive potting compound. After the shrinkable tubing is adhesively bonded onto this structure and the adhesive potting compound has cured, the shrinkable tubing insulates and seals the transition between the conductors and the heating element at the offset or shouldered end of the inner sheath, i.e. the portion of the conductor from which the insulating sheathing has been stripped off.
The conductors may include respective braided protective or shielding conductors that are arranged to lie over the inner sheath, but that have a length shorter than the current-carrying conductors. By subsequent measures, the ends of the strands of the protective conductor braid are combed out and twisted. Then a crimpable butt connector is used to electrically connect the twisted free end of the protective conductor braid to an additional extension conductor, by being crimped onto these two components. This additional extension conductor has a length extending to the ends of the current-carrying conductors of the heater band, and respective pin contacts are crimped onto the free ends of these respectively insulated conductors.
Next, a shrinkable tubing is shrunk over the electrical conductors, and then an adhesive potting compound is applied outside around the shrinkable tubing, over the transition area of the protective conductor braid at the location where the outer sheath has been removed from the heater band. The resulting structure is further covered by an additional shrinkable tubing that is shrunk into position thereon. The additional shrinkable tubing is adhesively bonded onto the underlying layered structure, and the adhesive potting compound is cured, whereby the additional shrinkable tubing then insulates the above described heater band interconnection at the offset or shouldered end of the outer sheath of the heater band. The heater band interconnection that is prepared in the above manner ensures that the prescribed sealing requirements in the field of aircraft construction are achieved.
Then, the heater bands are electrically connected to each other and/or to the electrical power supply network of the aircraft as follows. First, the pin contacts that were crimped onto the free ends of the electrical conductors and onto the additional extension conductors that were connected to the protective conductor braid, are then separately inserted or plugged into respective through-connect sockets. Thereby, all of the electrical connections of the heater bands to each other and to the on-board power supply network are realized by means of the through-connect sockets.
The heater band interconnection carried out in the above described manner results in a non-uniform and unwieldy geometry and involves several applications of an adhesive potting compound and plural shrinkable tubes forming sheaths. The process for forming the connection is rather complicated and time consuming because the connection structure is formed by manually applying the adhesive potting compound, and then fitting several shrinkable tubes thereon, and finally individually drying and curing each adhesive potting compound layer separately in an oven. There is also a danger that a uniform and constant quality cannot be achieved over a series of connections, whereby the sealing properties may be negatively influenced at the extreme low pressure conditions and drastic temperature variations that prevail in the aircraft. Moreover, a danger exists that the applied shrinkable tubes may crack or tear at various offset or shouldered or stepped locations of the non-uniform geometry. In that case, the sealing of the heater band interconnection, as well as the reliability of the heater band overall, will consequently be negatively influenced, whereby the power supply reliability of an entire integrated heating conductor interconnection system can be jeopardized.
Moreover, the above described conventional technology suffers the disadvantage that the electrical conductors of the heater band, without the protective conductor braid, are functionally laid out as extension conductors. Only the protective conductor braid is connected to an additional lengthening extension conductor by means of butt connectors. In this context, the conductors must be embodied to have the proper length, e.g. be cut to the proper length, and be insulated at each one of the connections.
The above described conventional measures require a considerable amount of time, effort and expense. Moreover, the danger exists that one or more strands of the conductor will be damaged, and the surface protection can be damaged. The manual application of the adhesive potting compound onto the conductors and the subsequent sliding or pushing of the shrinkable tubes onto the arrangement also add to the technological effort and expense. The application of the adhesive potting compound is absolutely indispensable for adhesively bonding the shrinkable tubes for ensuring the sealing effectiveness and for avoiding the possibility of capillary action. As a further disadvantage, the electrical assembly of the protective conductor braid and the additional extension conductor by means of a respective butt connector does not exactly define the position and the integration of this assembly within the heater band connection. Therefore, and since the butt connector includes a through-going axial hole, it is not possible to avoid a complete or 100% capillary action through the crimped butt connector.
The multiple drying and curing steps required by the adhesive potting compound for adhesively bonding the shrinkable tubes by means of heating in an oven further add to the technical complexity, effort and expense. Moreover, the heater element itself and the associated electrical conductors must be individually and collectively adhesively bonded and sealed with respective shrinkable tubes. A final heat treatment for an additional outer shrinkable tube or sheath, which provides additional sealing and the outer mechanical protection of the prepared heater band connection, further considerably increases the technological effort and expense.
For the above reasons, heater band connections cannot be economically and practically produced according to the methods and arrangements of the prior art. Moreover, the heater bands to be installed in an aircraft cannot be economically pre-fabricated according to the above described state of the art.